Since synthetic resins such as polymethyl methacrylate resins, polystyrene resins, and polycarbonate resins have excellent impact resistance and transparency, and are light and easily processed, they are used in skylight material of buildings, windows for vehicles, lamp lenses, instrument covers, and the like as a material substitute for glass. However, since synthetic resins have poor surface properties such as scratch resistance, chemical resistance, and weather resistance, compared to glass, the surface properties of the synthetic resins are modified. A method of coating heat-curable coating compositions such as a polyorganosiloxane-based composition and a melamine-based composition, and a method of coating polyfunctional acrylate-based active energy ray-curable compositions have been proposed as methods of improving the surface properties of synthetic resins.
Regarding these methods, Patent Literature 1 and 2 disclose the inventions of coating compositions obtained by mixing poly(meth)acrylate of mono- or poly-pentaerythritol, urethane(meth)acrylate having at least two (meth)acryloyl groups in a molecule, and poly[(meth)acryloyloxy alkyl]iso)cyanurate in a specific proportion.
Recently, in accordance with expansion of the outdoor application of synthetic resins, further improvement in the surface properties of synthetic resins is desired; in particular, high scratch resistance is demanded. However, the inventions recited in Patent Literature 1 and 2 do not satisfy the demand for high scratch resistance.
On the other hand, a method of adding inorganic material or inorganic-organic hybrid material to a coating composition is known as a method of improving the scratch resistance of the coating composition. For example, Patent Literature 3 discloses the invention of an abrasion-resistant coating composition comprising a reactive particle in which a radical polymerizable silane compound is chemically modified with a colloidal silica fine particle, poly[(meth)acryloyloxy alkyl]isocyanurate, urethane(meth)acrylate having at least two (meth)acryloyloxy groups and an alicyclic skeleton in a molecule, and a photopolymerization initiator. Although this invention can provide a cured coating film with scratch resistance, when the amount of reactive particles is increased to improve scratch resistance, the transparency of the resulting cured coating film is reduced.